1. There are 40 students in a class, of which 15 is in the math group, 18 is in the model airplane group, and 10 is in both groups. So how many people don't participate in both groups?

2.50 students stand in a row facing the teacher. The teacher asked everyone to press 1, 2,3, ..., 49,50 from left to right. Let the students who are calculated as multiples of 4 back off, and then let the students who are calculated as multiples of 6 back off. Q: How many students are facing the teacher now?

Answer;

1, because both groups 10 participated, so five people only participated in mathematics, and eight people only participated in airplane models. Plus that 10 makes 23 people, and 40-23= 17, 17 both groups did not participate.

2. 50÷4 is rounded to 12, and 50÷6 is rounded to 8. However, it should be noted that the multiple of 4 may be a multiple of 6 at the same time, so the common multiple of 4 and 6 should be calculated. There is 50 ÷12 (the least common multiple of 4 and 6) =4 (rounded), so

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